The present invention is a modification of a known assembly commonly known in the trade as a "roller tarp". Relevant examples of roller tarp assemblies are disclosed in U.S. Pat. No. 4,302,043, issued to J. R. Dimmer et al, and Canadian patent 1,132,168, issued to W. Michel.
These conventional roller tarp assemblies involve the following:
A rectangular tarpaulin;
The tarpaulin being secured along one side edge to a first side wall of the truck box;
The other side edge of the tarpaulin being secured to an elongate roller extending the length of the box;
The box having a support track frame extending laterally across the box opening, for supporting the roller as it moves across the opening. Typically one might have end frames, supported by the box end walls, a ridge pole bridging longitudinally between the end frames, and laterally extending, spaced apart hoops bridging the box side walls and ridge pole;
A universal joint, splined to the rear end of the roller, and a long crank connected to the universal joint to form a crank assembly, whereby a person standing on the ground may manually wind the roller using the crank assembly, to cause it to roll up or unroll the tarpaulin, thereby opening or closing the box opening; and
Means for enabling further tensioning of the tarpaulin, said means being operative to cooperate with the crank assembly to look up the roller when the opening is covered, so that a taut and continuing closure of the box may be achieved. In the Dimmer et al and Michel patents, such means comprise an elongated ledge, extending the length of the box. The ledge is mounted to the second 14 side wall of the box along its top edge and extends outwardly and slightly downwardly. The tarpaulin is sized so that, when it is fully unrolled, the roller hangs alongside the box side wall, just beneath the ledge. The roller can then be reverse-rolled to cause it to climb the tarpaulin and become trapped beneath the ledge. The roller is now restrained against further upward movement but it can still be reverse-rolled a further small amount, to wrap on more tarpaulin and tension it, so that it is taut across the box opening. The crank assembly may then be bent at the universal joint and the crank is secured flat against the box side or end wall by engagement with a suitable bracket. At this stage, the roller is looked against rotation because the crank assembly joined to it is fixed to the box, the tarpaulin is extended to cover the box opening, and the tarpaulin is pulled taut and close-fitting to the support track frame.
Now, there are disadvantages associated with the prior art system of trapping the reverse-rolled roller. The ledge itself is expensive, as it is usually fabricated from corrosion-resistant aluminum. Due to its protruding arrangement, it often is damaged by the blows and impacts to upper rim of the truck box that truck boxes commonly undergo. If damaged, the entire ledge must be removed and replaced. If the box is not completely square, there is no adjustment for front and back differential tension. And finally, parts cannot be quickly replaced or repaired by the owner.